Cell biologists have discovered a remarkable sequence of events associated with cell growth and proliferation. For many reasons we believe the injured lung may respond with such a sequence of events and these may be influenced by drugs. We will injure rat lungs with oxygen toxicity and then determine lung ornithine decarboxylase activity (ODC) at various times. Subsequently we will determine cyclic AMP, putrescine, spermidine and spermine content. The response will be modified by giving Epidermal Growth Factor (EGF), glucocorticoids and other drugs including inhibitors of ODC. The results will be correlated with autoradiography using 3H thymidine to determine which cells contribute to the observed biochemical changes.